The anti-inflammatory activities of extracts from the resins of four species of the plant family Burseraceae, Boswellia dalzielli, Boswellia carteri (gum olibanum), Commiphora mukul, and Commiphora incisa, were studied. The aqueous extracts of the resins of B. dalzielli, C. incisa, and C. mukul significantly inhibited both the maximal edema response and the total edema response during 6 h of carrageenan-induced rat paw edema. The octanordammarane triterpenes, mansumbinone and mansumbinoic acid, isolated from the resin of C. incisa, were separated and tested. Administered prophylactically, mansumbinone proved to be more than 20 times less potent than indomethacin and prednisolone in inhibiting carrageenan-induced rat paw edema. However, the molar potency of mansumbinoic acid was within one order of magnitude of those of indomethacin and prednisolone. The anti-inflammatory action of the acid on the carrageenan-induced edema was dose-related between 1.3 x 10(-5) and 2.5 x 10(-4) mol kg-1 when given before the inflammatory stimulus. The acid was able to reverse an established carrageenan-induced inflammatory response when administered 2 h after induction. Daily administration of mansumbinoic acid at a single dose level (1.5 x 10(-4) mol kg-1) significantly reduced joint swelling in adjuvant arthritis in rats. The results indicated that this compound is worthy of further investigation as an anti-inflammatory drug.